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1040 L. Bj .orkman et al. / Quaternary Science Reviews 21 (2002) 1039–1059 <strong>vegetation</strong> development, as a survival during cold stages (Bennett et al., 1991). However, neither the location of these glacial refugia is known in detail (Huntley <strong>and</strong> Birks, 1983; Willis, 1994), nor the areas where different tree species survived. Mid-altitude sites in, for instance Italy <strong>and</strong> the Balkans, where climatic conditions might have been favourable to support tree <strong>vegetation</strong> during cold stages, have been suggested as most likely refuge areas (e.g. Huntley <strong>and</strong> Birks, 1983; Bennett et al., 1991; Willis, 1992b, 1994). The majority of the pollen records available today fromsouthern Europe have been obtained from regional-scale sites which have a large pollen source area (Huntley <strong>and</strong> Birks, 1983; Willis, 1994). Therefore, they mainly show the regional, but not exactly the local <strong>vegetation</strong> development (Jacobson <strong>and</strong> Bradshaw, 1981; Sugita, 1993, 1994). Furthermore, many of these records have very low time resolution <strong>and</strong> are often restricted to the <strong>Holocene</strong> only. It is thus, difficult to locate exactly areas which could have acted as refugia <strong>and</strong> to reconstruct the local forest <strong>vegetation</strong>. Many trees show low pollen frequencies during the <strong>Lateglacial</strong> (Willis, 1994) <strong>and</strong> such low values are in general, difficult to evaluate without complementary data. A further problem is that many trees may have occurred in these refugia at very low densities. Conventional pollen analysis based on sediments from large sites does not allow detection of these low-density occurrences (Bennett, 1986; Kullman, 1995), but should be combined with plant macrofossil studies. However, such studies are yet rare fromsouthern central Europe <strong>and</strong> the Balkans (Willis, 1992a–c; Willis et al., 2000; Wohlfarth et al., in press). Another intriguing feature in <strong>Holocene</strong> palaeoecology is the remarkably rapid rate at which many tree species appear to have migrated from their glacial refugia (Huntley <strong>and</strong> Birks, 1983; Huntley, 1988). Such rapid migration rates are also shown, e.g. for Quercus <strong>and</strong> Fagus, which have a dispersal biology that would suggest a much slower migration. There is thus a possibility that some of these trees, which have been supposed to occur only in glacial refugia in southernmost Europe (e.g. Greece), also occurred further to the north. If this was the case, it would be easier to explain the seemingly rapid tree migration during the Early <strong>Holocene</strong>. Unfortunately, there is still not much evidence available to support this hypothesis, mainly because of a lack of detailed high-resolution studies (Willis, 1994). An area, which can be regarded as potentially important for the study of glacial refugia, <strong>and</strong> the local presence of tree species during the <strong>Lateglacial</strong>, is Romania. Large mid-altitude areasFparticularly in the Carpathian Mountains <strong>and</strong> adjacent areas in northwestern RomaniaFmay have had a suitable climate during the <strong>Lateglacial</strong>. Romania is also strategically situated in the middle of the migration routes from Greece <strong>and</strong> Bulgaria towards the north. Most tree species occurring today in northern Europe may have migrated through Romania (or from refugia in Romania) during the Early <strong>Holocene</strong>. If this was the case, it should be possible to detect <strong>early</strong> <strong>Holocene</strong> migration patterns in Romanian pollen records. Unfortunately, Romania is n<strong>early</strong> a ‘‘white spot’’ on the palaeoecological map of Europe (Willis, 1994; Berglund et al., 1996). Although pollen stratigraphic work has a long tradition in Romania (e.g. Pop, 1960), <strong>and</strong> a relatively large number of sites have been studied, the results are almost entirely published in national journals <strong>and</strong> therefore largely unknown outside Romania (e.g. Coldea, 1971; Diaconeasa <strong>and</strong> Stefureac, 1971; Pop, 1971; Diaconeasa <strong>and</strong> Farcas, 1996; Farcas, 1996). Most of these studies comprise only the <strong>Holocene</strong>, <strong>and</strong> all studies are characterised by low sampling resolution <strong>and</strong> a complete lack of radiocarbon dates. Age estimates have mainly been derived by comparing the <strong>vegetation</strong> development to the <strong>Lateglacial</strong> <strong>and</strong> <strong>Holocene</strong> <strong>vegetation</strong> zonation established for central Europe (Firbas, 1949, 1952). This makes it very difficult to compare the timing of the <strong>vegetation</strong>al development with the well-dated sequences frome.g. northern <strong>and</strong> western Europe (Berglund et al., 1996). Recently, however, Farcas et al. (1999) published a reconstruction of the regional <strong>Lateglacial</strong> <strong>and</strong> <strong>Holocene</strong> <strong>vegetation</strong> development, based upon pollen stratigraphy <strong>and</strong> AMS 14 C dates fromtwo sites in northeastern <strong>and</strong> southwestern Romania. Soon, AMS dates <strong>and</strong> pollen <strong>and</strong> macrofossil data will also be published froma site in northwestern Romania (Wohlfarth et al., in press), but the studied profile only covers the earliest part of the <strong>Lateglacial</strong>, c. 14,700–13,600 calibrated years BP. It is clear that additional palaeoecological investigations are urgently needed in Romania. New highresolution pollen studies, combined with AMS 14 C dating, will enable problems relating to glacial refugia <strong>and</strong> <strong>early</strong> <strong>Holocene</strong> tree migration to be addressed. Moreover, a network of sites at different altitudes should reveal local <strong>and</strong> regional differences in the composition of the <strong>Lateglacial</strong> <strong>and</strong> <strong>early</strong> <strong>Holocene</strong> <strong>vegetation</strong>. The chance of detecting refugia would, through such an approach, be far better than in a study performed on a single site only. The aimof this investigation is to present a spatially <strong>and</strong> temporally detailed reconstruction of the <strong>Lateglacial</strong> <strong>and</strong> Early <strong>Holocene</strong> <strong>vegetation</strong> development in the Gutaiului Mountains in northwestern Romania. The study is based on high-resolution pollen analyses <strong>and</strong> AMS 14 C measurements performed on cores from two relatively small <strong>and</strong> closely situated mid-altitude sites. In due course, plant macrofossil data also will be available, as well as pollen data covering middle <strong>and</strong> late <strong>Holocene</strong> <strong>vegetation</strong> changes.
L. Bj .orkman et al. / Quaternary Science Reviews 21 (2002) 1039–1059 1041 2. Study area The area with the two investigated former crater lakes (Preluca Tiganului <strong>and</strong> Steregoiu) is situated southeast of the small town of Negresti-Oas, on the western flank of the Gutaiului Mountains at an altitude of c. 700–900 ma.s.l. (Fig. 1). This massif is part of the Eastern Carpathian mountain chain, which stretches in a NNW–SSE direction <strong>and</strong> has peaks rising up to c. 1200–1400 ma.s.l. The first site, Preluca Tiganului (47148 0 83 00 N; 23131 0 91 00 E), is situated at an altitude of c. 730 ma.s.l., has an almost circular surface area of c. 1 ha <strong>and</strong> is drained by a small stream. Gently rising slopes surround the site to the east <strong>and</strong> south. South of the site, the Tigan Mountain attains an altitude of 843 m, <strong>and</strong> towards the north, fairly steep slopes lead down to the Talna valley, which is situated at c. 400 ma.s.l. The surrounding forest <strong>vegetation</strong> consists of relatively young Fagus st<strong>and</strong>s <strong>and</strong> recently (less than 20 years) planted Picea trees. In earlier investigations by Lupsa (1980) the site is described as an eutrophic to mesotrophic mire with a field layer dominated by grasses, sedges <strong>and</strong> herbs. Fig. 1. Location of the investigation area in northwestern Romania <strong>and</strong> a detailed map of the study area showing the position of the investigated sites, Preluca Tiganului <strong>and</strong> Steregoiu.
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